This is Heat Flux HF-30S Sensor (MTI.AWS.EK.HF.30S). A heat flux sensor is a thermopile, an electronic device that translates thermal energy into an electrical voltage proportional to the temperature gradient across its thermocouples' hot and cold junctions. 
EKO Instruments offers a selection of thin substrate heat-flux sensors in a range of different sizes and thicknesses, an ideal option for research and engineering applications as well as manufacturing control and monitoring processes.
The HF-30S is a thin foil extra-large heat-flow sensor covering 30 x 30 cm². Its size ensures properly averaged thermal conductivity results on adequate, flat surfaces without the potential risk of local hot spot effects or thermal bridges.